Field of the Invention
The present invention concerns a process and an apparatus for discharging and degassing a slurry from an attack tank. This process and apparatus may be used more particularly in the production of phosphoric acid.
Many chemical processes are known, which involve a reaction resulting in the formation of a slurry of greater or lesser thickness, for example leaching treatments, or operations for attacking an ore by means of an acid, as is the case in particular with the acid attack on a phosphate ore in the wet-process preparation of phosphoric acid. In such processes, the slurry which was formed in a reaction vessel or an attack tank must be discharged and filtered in order to separate the required product from the by-product or by-products.
Therefore, for proper operation of the process, it is necessary to supply the material to the filter as regularly as possible and for that purpose to degass the slurry and to avoid any air being entrained therewith when it passes from the attack tank to the filter. In addition, it is advantageous to be able to feed to the filter a slurry which enjoys the maximum degree of homogeneity.
There are various processes and apparatus for transporting slurries from the attack tank to the filter. In particular, a discharge system is known which comprises an overflow at the top of the tank, the overflow opening directly and perpendicularly into a vertical container connected to a pump which draws-in the slurry and passes it to the filter. The disadvantage of such a system is that air is entrained when the slurry goes from the overflow into the container.
In addition, in such a case, the slurry is discharged only at a single point in the attack tank so that there is the danger that the slurry discharged from the tank may not be perfectly homogeneous with the remainder of the slurry in the attack tank.